This invention relates to an adsorbent for the selective removal of organic sulfur compounds from hydrocarbon feedstocks, to a method for making the adsorbent, and to a process for using the adsorbent in producing a relatively sulfur free liquid hydrocarbon fuel.
Organic sulfur compounds are present in most gas and liquid refinery streams. H2S is the main moiety in gas streams. Mercaptans, organic sulfides, and disulfides are present in the liquid fractions obtained from the refining of crude oils like distillation naphtha and virgin cuts. Thiophenes, alkyl-thiophenes, benzothiophenes, and the like are produced by cracking of these organic sulfur compounds in processes such as thermal or catalytic cracking.
Due to environmental regulations, the amount of sulfur present in fuels has to be minimized. Besides, some downstream refining processes impose severe sulfur specifications in order to avoid catalyst deactivation. In both cases, refiners must accomplish reductions above 95% of the original feedstock sulfur.
Regardless of blending cases, in general, FCC naphtha, thermal cracking naphthas or reformate are the main components of final gasolines. Cracked naphtha represents 30 to 40 vol % of the gasoline blends. The rest of the gasoline components are butanes, alkylate, reformate, isomerizate, oxygenates, and coker naphthas in lower proportions. The sulfur concentration is lower than 20 wt ppm in the alkylate, while it is less than 1 wt ppm in the reformate or isomerizate. Therefore, it is the catalytic naphtha which is the main responsible component for the sulfur content in gasoline.
The potential use of fuel cells and on board reforming vehicles for year 2005 and beyond stresses the needs for fuels with sulfur specifications lower than 5 wt ppm. These new technologies are considering the installation of cartridges capable of sulfur removal ahead of the reformer or the fuel cell. A nonstop long-term tendency leads towards the production of ultra-low sulfur fuels.
Sulfur removal from liquid streams by adsorption or absorption methods are interesting due to their selective potentialities. So far, the available hydrotreatment technologies have limited performance with feedstocks which have octane number sensitivity to hydrogenation, such as cracked naphthas, due to their olefin and aromatic contents. On the other hand, those technologies affect the hydrogen balance in the refinery. Emergent technologies based on biodesulfurization, liquid extraction, oxidation and ultrasound are currently under development and their application is not conventional for the refiners.
It is therefore the primary object of the present invention to provide a sulfur selective adsorbent, which is not rapidly deactivated during use, even in the presence of mono olefins, dienes and aromatic compounds in the liquid hydrocarbon streams.
It is a further object of the invention to provide a process for removing sulfur compounds using a sulfur selective adsorbent.
It is a still further object of the invention to provide a method for making a sulfur selective adsorbent.
Other objects and advantages will appear hereinbelow.